High-strength concrete is concrete with a considerably higher compressive strength than ordinary structural concrete. According to the concrete standard EN 206, strength classes above C50/60 fall into this category. Where common concrete usually lies in classes C20/25 to C30/37, high-strength concrete therefore begins around C55/67 and runs up to C100/115 and higher.
How is it achieved?
A high strength results from a very dense, compact concrete structure:
- Low water-cement ratio — less water gives a denser mix
- Superplasticisers — keep the concrete workable nonetheless
- Fine additions — silica fume (microsilica) and fly ash fill the smallest voids
- Strong aggregate — high-quality, strong gravel or crushed stone
Advantages
- Slimmer structures — thinner columns and beams for the same load
- Larger spans — less self-weight per metre
- More floor area — smaller columns leave more usable space
- Durability — the dense structure better resists the ingress of moisture and chlorides
Points of attention
- More brittle behaviour — the higher the strength, the less deformation before failure; extra attention to reinforcement
- Fire behaviour — dense concrete can spall in a fire; measures are taken for this
- Placing — requires strict control of mix, pouring and curing
Application
High-strength concrete is used in high-rise buildings, bridges, heavily loaded columns and precast elements.
Related terms
- Concrete
- Compressive strength
- Concrete quality
- Microsilica
- Structural concrete
- Water-cement ratio
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